Question: I was on a recent flight out of DFW, and right after takeoff we had to fly around major storms that were producing baseball-sized hail and tornadoes. They closed the airport for about two hours right after our departure. Can planes fly through hail, and even a tornado?

- Submitted by reader Rod, Oklahoma City

Answer: Airplanes that fly through hail are usually damaged; therefore pilots avoid areas of hail. As an extreme example, in 1977, a Southern Airway DC-9 had both engines destroyed by hail, causing a forced landing.

Flying through a tornado could destroy an airplane; pilots avoid all thunderstorms -- particularly those producing tornadoes -- by a wide margin.

Q: Do pilots avoid flying through clouds? Or specific kinds of clouds?

- Gary D, Cleveland, Ohio

A: Flying into thunderstorms is not done, nor is flying around volcanic ash clouds (which is why that eruption in Iceland a few years ago was so disruptive to global aviation). Otherwise it is common to fly in clouds.

Q: Since clouds appear to be very light and float in the air, why do they cause a bumpy ride?

- Karin, Port St. Lucie, Fla.

A: It depends on the type of cloud. Cumulus clouds are caused by rising warm air; when an airplane flies into the rising current of air, it is bumpy.

What we see as clouds is condensed moisture. The cause of this condensation can vary. An example is lenticular clouds over the mountains that are caused by very high velocity winds. While they are beautiful, airplanes flying into them can be severely damaged by turbulence.

Q: On a recent flight through beautiful, partly cloudy skies, I noticed that in general, clouds are puffy and billowing on top, but flat on the bottom. Why is this so?

- Thom McLean, New Albany, Ind.

A: The puffy clouds you describe are cumulus clouds. They are formed by warm air rising in relatively moist air. This rising can cause a "boiling" effect that looks puffy. The flat bottom is where the moisture begins to become visible (near the dew point).

John Cox is a retired airline captain with U.S. Airways and runs his own aviation safety consulting company, Safety Operating Systems.